Teambuilder matching question.

I notice in teambuilder if I choose an off-meta champ for a position my projected wait time goes up regardless of whether the role is standard. So for example if I choose Karma mid mage, it'll say Very Long (and it will take a long time), but if I change my champ to Heimer it'll say Very Short/Short/Average and match me pretty quickly, despite being the same role and position. I'm just wondering how this works, since I typically think of teambuilder as being the place to try out less usual roles. Is the atypical pick being rejected by tons of team captains and the typical one getting ok'd immediately, or does the matchmaking system somehow prioritize matching team captains with champs played in their recommended role?

edit: just to clarify I'm not talking about getting kicked or leaving, but teams not getting matched at all.